Girlie is out with an urgent fix Movable Type users should make today!
If you are using Movable Type’s “Mail This Entry” feature on your blog, you are advised to rename your mt-send-entry.cgi file, or remove the feature entirely.
If you are not using the feature on your blog, you still need to either rename the script, disable it by changing the permissions, or remove it from your server altogether.
Spammers have discovered a means of using this script to send messages that will appear to be coming from your server.The best advice at this point seems to be to rename the mt-send-entry.cgi file. Ben Trott has a code modification fix you can make now, and the bug will be fixed in the next version of MT.
Kudos to Woody for bringing it to everyones attention.
Update: Movable Type has issued a revised version of the file. If you’re not using the functionality, there advice is to delete the file.